Polyol intermediate, polyesters made therefrom, and polyester coating compositions

ABSTRACT

There is provided a polyol intermediate that is the reaction product of neopentyl glycol with dimethyl glutarate in a 2:1 molar ratio. This reaction product is polyesterified with a phthalic acid reactant and neopentyl glycol to form a polyester resin. The resultant resin is admixed with an aminoplast and reduced to about 60-75 weight percent solids content with an aromatic hydrocarbon or a mixture of aromatic hydrocarbons to produce a thermosetting coating composition for metal substrates. Films made from this coating composition are hard and tough. They have excellent fabrication characteristics, high reverse impact resistance and excellent flexibility properties and solvent resistance.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of copending application Ser.No. 632,757, filed Nov. 17, 1975 now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention is directed to novel polyols, polyester resins madetherefrom, and thermosetting coating compositions containing suchpolyester resins and an aminoplast.

2. Description of the Prior Art

In U.S. Pat. No. Re. 27,279, there is disclosed a polyester (alkyd) of apolyol, a phthalic acid, and a dimer fatty acid. Insofar as is nowknown, the polyol intermediate of this invention has not been proposed.It has been found that polyester coatings made using this polyolintermediate have excellent properties including toughness, flexibility,and impact resistance.

SUMMARY OF THE INVENTION

This invention provides a polyol intermediate that is the reactionproduct of neopentyl glycol with dimethyl glutarate in a molar ratio of2 moles neopentyl glycol per mole dimethyl glutarate and at atemperature of between about 120° C. and about 210° C., until at leastabout 90 weight percent of theoretical methanol of reaction has beenremoved.

It also provides a polyester resin consisting essentially of, by weightof the total solids charged 35-40 percent of the aforedescribed polyolintermediate, 15-23 percent neopentyl glycol, and 40-45 percent phthalicacid reactant.

It further provides a coating composition comprising the aforedefinedpolyester resin and an aminoplast, using a weight ratio ofpolyester/aminoplast of about 90/10 to about 70/30, dissolved in anaromatic hydrocarbon solvent to a total solids content of between about60 and about 75 weight percent.

DESCRIPTION OF SPECIFIC EMBODIMENTS

An important component of the polyester resins of this invention is anovel polyol intermediate. This is the reaction product obtained byreacting neopentyl glycol with dimethyl glutarate in a ratio of 2 molesneopentyl glycol per mole of dimethyl glutarate. The reaction isessentially an alcoholysis reaction and is carried out at temperaturesof between about 120° C. and about 210° C., with the evolution ofmethanol. The reaction time will usually be between about 2 hours andabout 4 hours or until at least about 90 percent of the theoreticalmethanol has evolved. A catalyst, such as dibutyltin oxide, is generallyused in amounts of about 0.05-0.3 weight percent of the reactants.

EXAMPLE 1

Into a reactor provided with a condenser and a receiving vessel, werecharged 2 moles neopentyl glycol, 1 mole dimethyl glutarate, and 0.1weight percent, based on the weight of the reactants, dibutyltin oxide.The reaction mixture was heated to 140° C. under an inert gas (nitrogen)blanket and methanol started to evolve and was collected in thereceiver. The temperature was increased to about 200° C. over a periodof about 3 hours. Methanol was continuously collected as it evolved andthe reaction was continued until about 90 percent of the theoreticalmethanol had been collected.

Theoretically, the product of Example 1 would have the structure:##STR1## As described hereinafter, however, analysis has indicated thatthe product is a mixture of various components. It is possible that onecomponent could be a simple 1:1 molar reaction product having thestructure: ##STR2## It is also possible that some polycondensation couldoccur to give components having the general structure: ##STR3## whereinn is a small whole number from 2 to 6.

EXAMPLE 2

Gel permeation chromatography (GPC) was employed with 4' × 3/8" columnshaving pore sizes of 60A, 60A, 200A, 200A, to separate the components ofthe reaction product of Example 1. Neopentyl glycol was identified as acomponent by comparison with an authentic sample. High resolution gelpermeation chromotography was then employed using three 100A, and two500A, columns, each 25 cm. × 7.6 mm. i.d. The three peaks of highestmolecular weight components (the first three eluted) were recycled toimprove resolution. A dual detector system was used consisting of 254nm. (nonameter = one billionth of a meter) ultraviolet and arefractometer. Nuclear Magnetic Resonance spectra (each sample dissolvedin deuterochloroform) showed differences in structure of the components,particularly with regard to branching and hydroxyl content. A summary ofthe comparison of the components of the reaction product of Example 1 isset forth in Table 1.

                  TABLE I                                                         ______________________________________                                        Component  Area %                                                             (highest to lowest                                                                       of Peak                                                            molecular weight)                                                                        (GPC)     Identification                                           ______________________________________                                        1                        Ester with branching and                                                      hydroxyl groups                                      2              35%       Ester, less branching com-                                                    pared with peak #1 and less                                                   hydroxyl content                                     3                        Ester, considerably higher                                                    hydroxyl content compared                                                     with peaks #1 and #2                                 4              26%       Ester, similar to peak #3                                                     but lower molecular weight                           5              28%       Ester, similar to peak #4                                                     but lower molecular weight                           6              0.7%      Ester, lower molecular weight                        7              11%       Neopentyl glycol                                     ______________________________________                                    

The hydroxyl value of 371 and the number average molecular weight of 311of the reaction product of Example 1 conform to the theoretical valuesexpected for a simple diester with hydroxyl end groups, i.e., thetheoretical product. The data in Table I, however indicate a mixture ofcomponents having variations in structure and molecular weight.Accordingly, it will be appreciated that any designation assigned tothis reaction product, other than a definition comprising a recitationof the process of producing it, is not accurately descriptive of it.

The polyester resin of this invention is prepared by precondensation ofpolyol intermediate (Example 1) neopentyl glycol, and a phthalic acidreactant.

The phthalic acid reactant can be phthalic acid or anhydride,isophthalic acid, terephthalic acid and derivatives thereof, such ashexachlorophthalic acid or anhydride, or endomethylenetetrahydrophthalic acid or anhydride. Isophthalic acid, either alone orin admixture with lesser amounts of other phthalic acids is preferred.

The polycondensation reaction is carried out using, based upon the totalweight of charge, 35-40 percent polyol intermediate, 15-23 percentneopentyl glycol and 40-45 percent phthalic acid reactant. Preferably, acatalyst, such as dibutyltin oxide, is used. The polycondensationreaction is carried out at temperatures of 225°-250° C. for a period oftime of 6-8 hours. The reaction is complete when the Acid Number isbetween about one and about 20. Near the end of the reaction when in theorder of 90 percent of the water of reaction has been collected, removalof the remainder of the water can be facilitated by adding 2-4 weightpercent of an azeotroping agent, such as toluene or xylene.

EXAMPLE 3

A mixture of 37.3 parts by weight of the polyol intermediate (reactionproduct of Example 1), 20.1 parts by weight of neopentyl glycol, 13.1parts by weight of phthalic anhydride, and 29.4 parts by weight ofisophthalic acid was charged to a reactor equipped with a condenser andreceiving vessel. The mixture was heated to 240°-250° C. in 3-4 hoursand water of reaction was removed and collected as it formed. When about90 percent of the water of reaction had been collected, 2 parts byweight of toluene was added and the reaction was continued, usingazeotropic distillation to remove water and collecting water andreturning toluene to the reactor. When the Acid Number reached a valueof 1 (maximum), the product was diluted to 60 weight percent solids withcommercial mixture of aromatic hydrocarbon solvents having a boilingrange of 370°-510° F. (187.8°-265.6° C.).

It has been found that the reaction to prepare the polyol intermediatereaction product (Example 1) can be carried out in the presence ofexcess neopentyl glycol. Accordingly, in practice, it is preferred tocarry out the preparation of the polyol intermediate and thepolycondensation to polyester resin (Examples 1 and 3) sequentially inthe same reactor. Thus, the preparation of the polyol intermediate canbe carried out using all the neopentyl glycol required to make both thepolyol intermediate and the polyester resin. Subsequently, the phthalicacid reactant is added and the polycondensation is carried out. This isdemonstrated in the following example.

EXAMPLE 4

Into a reactor equipped with a condenser and receiving vessel, werecharged 267.35 lbs. of neopentyl glycol, 114.7 lbs. of dimethylglutarate, and 0.38 lb. of dibutyltin oxide. The reactants were heatedto 140° C. under a nitrogen gas blanket and methanol commenced toevolve. It was continuously collected over a 2-3 hour period while thetemperature was increased to 200° C., until 90 percent of thetheoretical methanol (45.53 lbs.) had been collected.

Then, there were charged 77.08 lbs. phthalic anhydride, 172.56 lbs.isophthalic acid and 0.25 lb. dibutyltin oxide. The reactants wereheated to 240°-250° C. in 3-4 hours and water of reaction was collected.About 1 hour after a temperature of about 240° C. had been reached, 90percent of the water had been collected. The condenser was converted toazeotropic distillation using a trap to separate and remove water and toreturn the azeotroping agent to the reactor. Toluene (14.4 lbs.) wasadded and azeotropic distillation was carried out until the Acid Numberof the reaction mixture was 1 or less. The total water collected was46.79 lbs. The resulting polyester resin was diluted to 60 weightpercent solids with 345.6 lbs. of a commercial mixture of aromatichydrocarbon solvents having a boiling range of 370°-510° F.(187.8°-265.6° C.), forming a polyester resin solution for use in acoating formulation.

EXAMPLE 5

Into a reactor equipped with a condenser and receiving vessel, werecharged 251.17 lbs. of neopentyl glycol, 121.66 lbs. of dimethylglutarate, and 0.38 lb. of dibutyltin oxide. The reactants were heatedto 140° C. under a nitrogen gas blanket and methanol commenced toevolve. It was continuously collected over a 2-3 hour period while thetemperature was increased to 200° C., until 90 percent of thetheoretical methanol (48.51 lbs.) had been collected.

Then, there were charged 81.77 lbs. phthalic anhydride, 183.06 lbs.isophthalic acid and 0.26 lb. dibutyltin oxide. The reactants wereheated to 240°-250° C. in 3-4 hours and water of reaction was collected.About 1 hour after a temperature of about 240° C. had been reached, 90percent of the water had been collected. The condenser was converted toazeotropic distillation using a trap to separate and remove water and toreturn the azeotroping agent to the reactor. Toluene (14.4 lbs.) wasadded and azeotropic distillation was carried out until the Acid Numberof the reaction mixture was 14-18. The total water collected was 49.79lbs. The resulting polyester resin was diluted to 60 weight percentsolids with 345.6 lbs. of a commercial mixture of aromatic hydrocarbonsolvents having a boiling range of 370°-510° F. (187.8°-165.6° C.),forming a polyester resin solution for use in coating formulation.

COATING COMPOSITIONS

The polyester resin can be thermoset using a conventional aminoplastcross-linking agent. Such agents are well known in the art. There can beused any of the thermosetting alkylated aminoplast resins, such as theurea-aldehyde resins, the melamine-aldehyde resins, thedicyandiamide-aldehyde resins and other aminoplast-aldehyde resins suchas those triazine resins produced by the reaction of an aldehyde withformoguanamine, ammeline, 2-chloro-4, 6-diamino-1,3,5-triazine,2-phenyl-p-oxy-4, 6-diamino-1,3,5-triazine,6-methyl-2,4-diamino-1,3,5-triazine; 2,4,6-trihydrazine-1,3,5-triazine,and 2,4,6-triethyl-triamino-1,3,5-triazine. As aldehydes used to reactwith the amino compound to form the resinous material, one may use suchaldehydes as formaldehyde, acetaldehyde, crotonic aldehyde, acrolein, orcompounds which engender aldehydes, such as hexamethylenetetramine,paraldehyde, paraformaldehyde, and the like.

A preferred class of aminoplasts is a melamine-formaldehyde resin thathas been alkylated with methanol, butanol, or a mixture of methanol andbutanol. Typical of this class is hexamethoxymethyl melamine. Ingeneral, a solvent such as butanol or ethoxyethyl acetate may be used.

Although not essential, it is preferable to use an acid cross-linkingcatalyst, such as p-toluenesulfonic acid. Other suitable catalystsinclude acid phosphates, such as methyl acid phosphate and butyl acidphosphate; acid pyrophosphates, such as dimethyl acid pyrophosphates;organic acid sulfate esters; and other organic sulfonic acids.

Although a pigment is not necessary, it is preferred to incorporate apigment into the coating composition of this invention. The preferredpigment is titanium dioxide for white coats, but any well known fillerpigment can be used, such as zinc oxide, bentonite, talc, silica,ochers, and chrome yellows or greens.

Other well known adjuvants may be added, such as flow control agents andwaxes. A preferred flow control agent is sodium dioctyl sulfosuccinate,but others utilizable include sodium dihexyl sulfosuccinate, sodiumdiamyl sulfosuccinate, isopropyl naphthalene sulfosuccinate, andsorbitan monolaurate, monopalmitate, or monooleate. Waxes, if used, areadded as slurries or emulsions of petroleum (paraffin) wax, naturalwaxes such as montan wax, beeswax, and carnauba wax, or synthetic waxessuch as polyethylene wax.

To prepare the final coating composition the polyester resin solution isadmixed with the aminoplast mixture. These components will usually beblended using between about 70 and about 90 parts by weight of polyesterresin solution to between about 30 and about 10 parts by weightaminoplast mixture. Other ratios can be used, bearing in mind, however,that higher aminoplast concentrations tend to increase brittleness ofthe final baked finish and that lower aminoplast concentrations tend toincrease back temperature or bake time, or both. The final productshould have a solids content of between about 60 and about 75 wt.%.

These coating compositions can be applied to the desired substrate assuch or, in some cases, they may be diluted ethoxyethyl acetate oraromatic solvent or a 50/50 mixture thereof. After application thecoating is baked for about 3 seconds to about 5 minutes at between about250° F. and about 600° F. A preferred bake is for about 40 seconds at560° F.

Suitable substrates are paper, metallic foil and can stock metals(approximately 10 mil stock). The coating can be applied by roll coat,flow coat or gravure coat.

EXAMPLE 6

The polyester resin solution (Example 4) was mixed withhexamethoxymethylmelamine aminoplast to provide a solution containing85/15 weight ratio polyester/aminoplast on a non-volatile basis. Theproduct was pigmented with TiO₂ at about 0.85/1.00 pigment/binder weightratio. About 0.5 weight percent p-toluene sulfonic acid was added as acatalyst.

The resultant coating composition was applied to 26 gauge hot dipgalvanized steel panels and cured for about 40 seconds at 560° F. Aftercooling, the panels were subjected to various tests with the results setforth in Table II.

                  TABLE II                                                        ______________________________________                                        Flexibility, Olsen   #8                                                       Wedge-bend Flexibility                                                                             No tape pull-off                                         Fabrication 180° Bend                                                                       OT - No flake (10)                                       Impact Resistance    80" lbs. - reverse                                       Pencil Hardness      H-2H                                                     Solvent Resistance (MEK rubs)                                                                      50 MEK double rubs                                       ______________________________________                                    

Impact resistance was determined in accordance with ASTM DesignationD2794-69. The other test procedures were as follows:

Flexibility, Olsen -- A Tinius Olsen Testing Machine equipped with a 1inch diameter forming die and a 7/8 inch diameter ball is used. The testpanel is clamped between the ball and the die and load is applied tofracture the metal. Scotch brand tape is applied to the formed cup andremoved quickly. The adhesion rating is made by comparison with eightstandard rating photographs, wherein #1 is the poorest rating and #8 isthe best.

Wedge-bend flexibility -- The panels are bent into a U-shape and placedunder the hinge of the tester which slopes downward from 1/8" to 0" andpressed. This results in a wedge-bend sloping from 0" to 1/8" over adistance of 100 mm. Scotch tape is then applied to the wedge and removedquickly. Cracking or removal of the film is measured in millimetersalong the bend from 0" toward the 1/8" and recorded as percent failure.

Fabrication 180° Bend (OT Bend) -- The panel is manually bent into aU-shape. A number of thicknesses of the substrate (in this case, nothicknesses or OT) are placed in the bend area and the entire assemblyis placed in the jaws of a press and pressed. Scotch tape is appliedacross the bend and removed quickly. The adhesion of the coating afterbending is rated on a scale of 0 to 10 with 10 representing perfect,i.e., no coating was pulled off with the tape.

Pencil hardness test -- A set of pencils ranging from 6B (soft) to 6H(hard) are used, starting with the hard end of the set. These pencilsare pushed in turn into the film. The first pencil which crumblesinstead of penetrates indicates the pencil hardness.

MEK Double Rubs -- A pad of felt (2" square) soaked in MEK (methylethylketone) is rubbed back and forth across the coated surface, while thepanel is resting on a firm surface. Each stroke is 21/2-3" in length ata uniform pressure of about 900 grams and at a rate of about 100 rubsper minute. The pad is re-soaked with MEK after 50 double rubs, orbefore, if increase in friction makes it necessary. One double rub isconsidered as one back and forth stroke. Fifty double rubs should onlyslightly dull the surface in the center area of the rub.

EXAMPLE 7

Following the blending procedure of Example 6, a pigmented coatingcomposition was made using the polyester resin solution of Example 5.This composition was applied to electrocoated tin plated steel and curedfor about 41 seconds at 560° F. Test results are set forth in Table III.

                  TABLE III                                                       ______________________________________                                        Flexibility, Olsen   #8                                                       Fabrication 180° Bend                                                                       OT - No flake (10)                                       Pencil Hardness      H                                                        Solvent Resistance (MEK rubs)                                                                      60+                                                      ______________________________________                                    

Although the present invention has been described with preferredembodiments, it is to be understood that modifications and variationsmay be resorted to, without departing from the spirit and scope of thisinvention, as those skilled in the art will readily understand. Suchmodifications and variations are considered to be within the purview andscope of the appended claims.

What is claimed is:
 1. A coating composition comprising the polyesterresin which consists essentially of, by weight of the total solidscharged, 35-40 percent of a polyol intermediate that is the reactionproduct of neopentyl glycol with dimethyl glutarate in a molar ratio of2 moles neopentyl glycol per mole dimethyl glutarate and at atemperature of between about 120° C. and about 210° C., until at leastabout 90 weight percent of theoretical methanol of reaction has beenremoved, 15-23 percent neopentyl glycol, and 40-45 percent phthalic acidreactant; said resin having an Acid Number between about 1 and about 20,and an aminoplast, using a weight ratio of polyester/aminoplast of about90/10 to about 70/30, dissolved in an aromatic hydrocarbon solvent to atotal solids content of between about 60 and about 75 weight percent. 2.The coating composition of claim 1, wherein said phthalic acid reactantis a mixture of phthalic anhydride and isophthalic acid and saidaminoplast is hexamethoxymethylmelamine.
 3. The coating composition ofclaim 1 containing a pigment.
 4. The coating composition of claim 3,wherein the pigment is TiO₂ in a pigment/binder ratio of about 0.85/1.5. The coating composition of claim 2 containing TiO₂ pigment in apigment/binder ratio of about 0.85/1.